Composition for forming a patterned metal film on a substrate

ABSTRACT

A composition for forming a patterned thin metal film on a substrate is presented. The composition includes metal cations; and at least one solvent, wherein the patterned thin metal film is adhered to a surface of the substrate upon exposure of the at least metal cations to a low-energy plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No.PCT/US2015/056438 filed on Oct. 20, 2015 which claims the benefit ofU.S. Provisional Application No. 62/066,392 filed on Oct. 21, 2014, thecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to techniques and an inkcomposition for forming conductive material on substrates, and inparticular to techniques for fabricating or printing thin patternedmetal films on substrates.

BACKGROUND

The field of organic and printed flexible electronic devices is a fastgrowing field with a wide range of applications in the fields of lightemission, light-energy conversion, microelectronics, and macroelectronics. For example, organic field-effect transistors (OFETs) andorganic light-emitting diodes (OLEDs) have garnered great interest dueto their technological potential as a cheap alternative to inorganic,e.g. silicon-based, thin-film transistors and diodes. Further, organicelectronics may provide electronic circuits with new attractiveproperties, such as flexibility and transparency. The structure of anorganic electronic device may include a single layer or multiple layersof organic materials and patterned metal features (e.g., electrodes).However, the formation of electrical contacts with the organic layershas not yet matured to an efficient industrial fabrication process. Thisis due mainly to the cost, materials, and fabrication techniques thatare being used.

Specifically, utilization of organic materials in electronic devices orcircuits places certain restrictions on the fabrication processes whichultimately limit the functionality of the resulting fabricated organicelectronic devices. This is due to the low decomposition temperature oforganic compounds as well as their relatively high susceptibility toundesired chemical reactions that destroy their functionality arisingduring fabrication.

The physical vapor deposition (PVD) technique is one of the fabricationtechniques utilized for forming metal electrodes with organic layers.The PVD technique uses a physical process, such as heating orsputtering, to produce a vapor of material, which is then deposited onthe object which requires coating. The PVD process is typically used inthe manufacture of items which require thin films for mechanical,chemical or electronic reasons. Examples include semiconductor devicessuch as thin film solar panels.

The PVD process is mainly based on vapor deposition approaches that areprone to damaging the organic active components. For example, when thePVD method is utilized, the metal material is evaporated from a solidsource onto a substrate located at a certain distance from the source.Further, when the PVD is utilized, the whole process is performed in avacuum chamber. During the process, high-energy metal atoms “bombard”the substrate surface and are able to penetrate into organic materials,thereby substantially damaging the organic surface. The damage and theloss of the evaporated metal associated with the use of the PVD processlimits the cost efficiency of the PVD method for preparing organicelectronic devices.

Another fabrication technique utilized for forming metal electrodesorganic layers is chemical vapor deposition (CVD). During a CVDfabrication process, the organic substrate is exposed to highly reactiveand aggressive reagents in the reaction chamber which are harmful to theorganic substrates.

Other techniques for forming metal films on substrates include inkjetprinting, screen printing, aerosol printing, and nanoimprintlithography, all of which use nanoparticle dispersion. In mostimplementations, the “ink” used in these printing processes is based onorganic-ligand stabilized dispersions of metal nanoparticles or metalorganic compounds. The ink-based printing of metal films can beintegrated in large-scale manufacturing systems for electronic devices.However, existing ink-based printing processes are very expensive due tothe cost of such ink compositions. Specifically, the manufacturing ofthe ink is expensive because of the number of processing stepsassociated with synthesis, dispersion, purification, and concentrationof the ink solution. Further, using currently available ink solutionsrequires heating of the solution when applied on the substrate in orderto form the film.

For example, an ink composition for printing on a ceramic substrateutilized in existing solutions includes in part sub-micron particlesacting as a binding composition and having a melting point below 600° C.Such a binding composition becomes an integral part of the substrateupon exposure to temperatures above the melting point of the bindingcomposition.

It would therefore be advantageous to provide a method, system and anink composition for forming a patterned metal film on a substrate thatwould overcome the deficiencies of the prior art.

SUMMARY

A summary of several example embodiments of the disclosure follows. Thissummary is provided for the convenience of the reader to provide a basicunderstanding of such embodiments and does not wholly define the breadthof the disclosure. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments nor to delineate the scope of anyor all aspects. Its sole purpose is to present some concepts of one ormore embodiments in a simplified form as a prelude to the more detaileddescription that is presented later. For convenience, the term “someembodiments” may be used herein to refer to a single embodiment ormultiple embodiments of the disclosure.

The disclosed embodiments include an ink composition for forming apatterned thin metal film on a substrate. The ink composition comprisesmetal cations; and at least one solvent, wherein the patterned thinmetal film is adhered to a surface of the substrate upon exposure of theat least metal cations to a low-energy plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter disclosed herein is particularly pointed out anddistinctly claimed in the claims at the conclusion of the specification.The foregoing and other objects, features, and advantages of thedisclosed embodiments will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

FIG. 1a through 1e are diagrams illustrating the process of forming athin patterned metal film on a substrate according to an embodiment

FIG. 2 is a flowchart illustrating a method for forming thin patternedmetal films on substrates using plasma according to an embodiment

FIG. 3 is a block diagram of a machine structured to form thin patternedmetal films on substrates according to the various embodiments disclosedherein.

FIG. 4 is a scanning electron microscope (SEM) image of a silver metalfilm formed on a silicon substrate formed according to an embodiment.

FIG. 5 is a SEM image of a gold metal film formed on a PET substrateformed according to an embodiment.

DETAILED DESCRIPTION

It is important to note that the embodiments disclosed herein are onlyexamples of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedembodiments. Moreover, some statements may apply to some inventivefeatures but not to others. In general, unless otherwise indicated,singular elements may be in plural and vice versa with no loss ofgenerality. In the drawings, like numerals refer to like parts throughseveral views.

According to the disclosed embodiments, an ink composition, a machine,and a process for forming thin patterned metal films on a substrate aredisclosed. The process for forming the metal films may be anyfabrication, manufacturing, and/or printing process. The disclosedprocess is based, in part, on exposing a substrate having portionsthereof coated with the ink composition to plasma for a predefinedperiod of time.

The plasma is low energy plasma, such as radio frequency (RF) plasma oranother non-thermal plasma. The use of low energy plasma enables theconduction of a chemical reaction without creating high temperatures onthe surface of the substrate. Thus, the disclosed process would notdamage or otherwise harm the surface or deeper layers of the substrate.It should be noted that the metal film includes any metal feature thatcan be adhered or bounded to the film. Furthermore, “metal” of the metalfilm as referred to herein includes any metals, metal alloys, and/ormixtures of various types of metals.

The patterned metal features may be electrodes or any passive electricalelement. Therefore, the forming process and ink composition disclosedherein allows for low-cost and mass-manufacturing of electronic devicesincluding, but not limited to, frequency identification tags (RFIDs),electronic sensors, integrated electronic circuits, flexible displays,photovoltaic devices, organic field effect transistors (OTFTs or OFETs),organic light emitting diodes (OLEDs), and the like.

FIGS. 1a through 1e are exemplary and non-limiting diagrams illustratinga process of forming a thin patterned metal film on a substrateaccording to an embodiment. Referring to FIG. 1 a, the process isperformed over a substrate 110. The substrate 110 can be made ofmaterials including, but not limited to, organic materials, ceramic,silicon, glass, cellulose nanofibers, and the like. In addition, thesubstrate 110 may be made of materials sensitive to high temperaturessuch as, but not limited to, polyethylene terephthalate (PET),polyimide, polyethylene naphthalate (PEN), and the like. Such substratesare typically in a form of films or sheets. In an embodiment, thesubstrate 110 may be prepared solely from organic materials, solely frominorganic materials, or from a combination or hybrid of organic andinorganic materials.

In an embodiment, prior to film formation, the substrate 110 mayoptionally be first cleaned using a proper procedure for cleaningsubstrates. In an exemplary embodiment, a sonication cleaning procedureusing a cleaning solution (such as, e.g., Isopropyl alcohol) can beutilized. It should be noted that other cleaning procedures may beutilized without departing from the scope of the disclosed embodiments.One of ordinary skill should be familiar with other cleaning proceduresthat can be used for this purpose.

The substrate 110 is treated so only desired areas of the surface of thesubstrate 110 will react with, or be exposed to, an ink composition,when such composition is applied. The desired areas include one or morepatterns where the patterned metal film(s) will be formed. In certainimplementation, a mask is first placed on the substrate's surface tomark the desired areas. Such a mask can be further used when applyingthe ink composition on the substrate. In an embodiment, such treatmentis performed by exposing the substrate 110 to a low-energy andnon-thermal plasma, such as Oxygen plasma. To this end, the substrate110 is placed in a first chamber 101 and exposed to Oxygen plasma in afirst exposure as determined by a first set of exposure parametersincluding, for example, power, RF frequency, gas flow rate, and timeduration. The values of the first set of exposure parameters aredetermined based, in part, on the type of the substrate 110.

In certain embodiments, an atmospheric plasma (e.g., of Oxygen) isutilized. Exposing the substrate to the atmospheric plasma can beperformed using an atmospheric plasma jet, an atmospheric plasma spray,a dielectric barrier discharge, and the like. Thus, in this embodiment,the chamber 101 is not required. As noted above, the low-energy andnon-thermal plasma are used regardless of whether the chamber 101 isused. The temperature range of the substrate that is exposed to theplasma is between 50° C. and 70° C.

Referring to FIG. 1 b, after cleaning and/or treating the substrate 110,a mask 120 is applied to create the desired pattern. The mask 120ensures that the ink composition is applied to the substrate 110 only inthe desired pattern to form the thin patterned metal film. In thisexample, the pattern is a rectangular stripe.

According to some embodiments, shadow masking is utilized such that apolymeric mask 120 is applied directly to the surface of the substrate110. In such embodiments, voids (spaces) in the mask 120 define wherethe ink composition contacts the substrate's 110 surface. As notedabove, the mask 120 can also be used for pre-treating the substrate.

Referring now to FIG. 1c , the ink composition 130 is applied on thesubstrate 110, specifically to areas not covered by the mask 120. In anembodiment, the ink composition 130 is applied by a means including, butnot limited to, drop-casting, spin-coating, spray-coating, immersion,flexography, gravure, inkjet printing, aerosol jet printing, contactimprinting, and the like.

Referring now to Referring to FIG. 1d , the substrate 110 including themask 120 and the ink composition 130 is placed in a second chamber 102and exposed to plasma gas in a second exposure as determined by a secondset of exposure parameters. The plasma gas utilized in the second phasein the chamber 102 includes an inert gas such as Argon, Nitrogen, andthe like. The second exposure parameters include, for example, power,frequency, gas flow rate, and time duration. The values of the secondset of exposure parameters are determined based, in part, on the type ofthe substrate 110, the ink composition 130, and/or the means ofapplication. It should be noted that the chamber 102 may be a vacuumchamber. It should be further noted that the chambers 101 and 102 may bethe same chamber such that the first and second exposures differ only inthe type of gas flowing through the chamber in each phase. The mask 120may be removed after applying the composition 130. The mask 120 mayfurther remain for the duration of the second exposure and removedthereafter.

In certain embodiments, an atmospheric plasma of an inert gas such as,e.g., Argon or Nitrogen plasma, is utilized also during the secondexposure. Exposing the substrate to the atmospheric plasma can beperformed using an atmospheric plasma jet, an atmospheric plasma spray,a dielectric barrier discharge, and the like. Thus, in this embodiment,the chamber 102 is not required. As noted above, the low-energy andnon-thermal plasma are being used regardless if the chamber 102 is beingused. Therefore, the temperature range that the substrate is exposed to,also in this phase, is between 50° C. and 70° C.

Referring now to FIG. 1 e, as a result for the exposure to the Argon orNitrogen plasma, the substrate 110 is covered by the thin patternedmetal film 140 shaped in the pattern of the mask 120. The chemical andelectrical properties of the thin patterned metal material film 140 aredetermined based on the chemical properties of the ink composition 130and the substrate 110 as well as based on the exposure parameters of theexposure to the Argon or Nitrogen plasma. For example, the thickness ofthe patterned metal film 140 can be controlled by modifying theconcentration of the metal in the ink composition 130, the duration ofthe exposures to the plasma in the second phase, and/or the number ofplasma exposure “treatments”. Additional examples for chemical andelectrical properties are described further herein below.

FIG. 2 is an exemplary and non-limiting flowchart 200 illustrating amethod for forming thin patterned metal films on substrates using plasmaaccording to one embodiment. At S210, the substrate is cleaned using acleaning procedure. The cleaning procedure is determined based on thetype of substrate. At S220, the certain patterned areas of the substrateare pre-treating by being exposed to a first plasma source of alow-energy and non-thermal plasma.

In an embodiment, the first plasma source provides Oxygen plasma and isset according to a first set of exposure parameters. As noted above,these parameters include, for example, power, frequency, gas flow rate,and time duration. The values of the first set of exposure parametersare determined based, in part, on the type of the substrate. At the endof S220, only desired areas of the surface of the substrate will reactwith the ink composition. In certain embodiments, S210 and/or S220 areoptional. That is, the process disclosed herein can be performed onpre-treated substrates. Such substrates can be pre-treated by adifferent machine or at a different facility.

At S230, a mask is placed on the treated substrate. In an embodiment,shadow masking is utilized such that a polymeric mask is applieddirectly to the surface of the treated substrate. In such embodiments,voids (spaces) in the mask define where the ink composition contacts thesubstrate surface. According to another embodiment, the treatedsubstrate's surface is selectively modified using, for example,photolithographic techniques. According to some embodiments, thesubstrate includes photoactive functional groups. Thus, once a mask isapplied to the substrate, the substrate's surface may be irradiated withany appropriate type of radiation such that only the photoactive groupsnot covered by the mask are irradiated. This masking technique createstreated and non-treated areas on the substrate. As a result, the treatedareas have higher or lower affinity to the components of the inkcomposition than the non-treated areas.

According to further embodiments, micro-contact printing,chemo-mechanical surface patterning, selective chemical modification,and template assisted patterning or any other appropriate procedure maybe utilized for the partial modification of the surface of thesubstrate. It should be noted that, in certain embodiments, S230 isoptional.

At S240, the ink composition is applied on the void areas of the mask.In an embodiment, the ink composition can applied by means including,but not limited to, a drop-casting, spin-coating, spray-coating,immersion, flexography, gravure, inkjet printing, aerosol jet printing,contact imprinting, and the like.

At S250, the substrate including the ink composition is exposed to asecond plasma source as determined by a second set of exposureparameters. In an embodiment, the second plasma source provides Argon orNitrogen plasma. In certain embodiments, the same chamber is used forboth the first and second plasma sources. In an optional embodiment, thechamber for the second plasma source is a vacuum chamber. In a furtherembodiment, the first plasma source may be the same as the second plasmasource.

In yet another embodiment, the second plasma source utilized in S250 isatmospheric plasma of inert gas. Exposing the substrate to theatmospheric plasma can be performed using an atmospheric plasma jet, anatmospheric plasma spray, a dielectric barrier discharge, and the like.In all of the above noted embodiments, the second plasma source is ofthe low-energy and non-thermal plasma.

The second set of exposure parameters include power, frequency, gas flowrate, and time duration. The values of the second set of exposureparameters are determined based, in part, on the type of the substrate110, the ink composition 130, and/or the means of application.

As a non-limiting example, the values of the second set of exposureparameters may be as follows: the power is between 5 W (watt) and 600 W,the plasma RF frequency is between 50 Hz and 5 GHz, the gas flow rate isbetween 2 SCCM and 50 SCCM, and the exposure time is between 1 secondand 5 minutes.

It should be noted that the plasma RF frequency and the operation powerare chosen according to the reduction potential of the metal. Generally,metals with higher reduction potentials require lower plasma RFfrequencies and operation powers. The time of exposure is determinedaccording to the metal-cation concentration in the composition, thereduction potential of the metal, and/or the gas flow rate. It is notedthat, generally, lower metal-cations concentrations, as well as metalswith higher reduction potentials and greater gas flow rates, require ashorter plasma exposure time, since at such conditions the rate ofprecipitation is higher.

In certain embodiments, S250 may be repeated a predefined number ofcycles, and the second set of exposure parameters may be set todifferent values for each cycle. In an embodiment, the number of cyclesmay be between 2 and 10. As noted above, the number of cyclesdetermines, in part, the thickness of the metal.

Once the plasma exposure cycle(s) is completed, the substrate may beremoved from the chamber. At this point, the ink composition has beenconverted to a patterned thin metal film, which is adhered to thesubstrate. As will be discussed herein, the ink composition may becomposed of different metal cations, and different contractions thereof.The resulting thin metal film may be comprised of various types ofmetals and/or alloys. According to some embodiments, the thickness ofthe thin metal film is between 0.02 μm and 2 μm.

As noted above, the chemical and electrical properties of the patternedthin metal film are determined based on the chemical properties of thecomposition and the substrate and/or the values of the plasma exposureparameters.

FIG. 3 shows an exemplary and non-limiting block diagram of a machine300 structured to form thin patterned metal films on substratesaccording to the various embodiments disclosed herein. That is, themachine 300 can also serve as a printing machine, a fabrication machine,a manufacturing machine, and the like. The machine 300 can be utilizedfor mass-production of electronic devices including, for example, RFIDs,electronic sensors, integrated electronic circuits, flexible displays,photovoltaic devices, organic field effect transistors, OLEDs, and thelike.

According to some embodiments, the machine 300 includes a plasma jet310, a nozzle 320 coupled to a container 330 containing the inkcomposition, and a controller 340. The plasma jet 310 is connected toone or more containers 350-1, 350-n that are the sources for thedifferent plasma gas. For example, containers may include Argon Plasma,Oxygen plasma, Nitrogen plasma, and the like. The containers 350 may ormay not be part of the machine 300. The plasma jet 310 is a means fordispensing atmospheric pressure plasma. The plasma jet 310 can bereplaced by an atmospheric plasma with corona discharges, and dielectricbarrier discharges. The movement of the plasma jet 310 is controlled bya moving arm 315.

In certain embodiments, when vacuum (or low-pressure) plasma isutilized, the plasma jet 310 is a replaced by a vacuum chambercontrolled by a vacuum pump (not shown).

The nozzle 320 may be any means for applying the ink composition in thecontainer 330 on the substrate 375. The nozzle 330 may be utilized fordrop-casting, spin-coating, spray-coating, immersion, flexography,gravure, inkjet printing, aerosol jet printing, contact imprinting, andthe like, and the like. The nozzle 330 may be connected to a moving arm335 to follow a specific pattern.

In certain embodiments, the machine 300 further includes a masking means360 for applying the mask on the surface of the substrate. The maskingmeans 360 may be also connected to a moving arm 365. The movement of themasking means 360 is controlled by the moving arm 365.

The controller 340 is configured to control the operation of the variouscomponents of the machine 300. For example, the controller 340 can setthe exposure parameters for the plasma jet 310, select a plasma source,control the injection casting of the composition, control the movementof the various moving arms, and so on.

The controller 340 can be realized as one or more general-purposemicroprocessors, multi-core processors, microcontroller, digital signalprocessors (DSPs), field programmable gate array (FPGAs), programmablelogic devices (PLDs), gated logic, discrete hardware components, and thelike. The controller 340 may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the controller, cause the controller toperform the various functions described herein.

According to various disclosed embodiments, an ink composition forforming thin metal films on substrate is disclosed. The ink compositionmay be in a form of a solution, dispersion, suspension, gel, or colloid.

In its basic form, the ink composition includes metal cations with atleast one type of solvent. According to some exemplary embodiments, themetal cations are M(NO₃)_(n), M(SO₄)_(n), MCl_(n), and H_(m)MCl_(n+m),where “M” is a metal atom (or any appropriate metal alloy) with avalence of “n”, H is hydrogen, NO₃ is nitrate, SO₄ is sulfate, Cl ischloride, and “m” is a valence of the counter ion. In a furtherembodiment, the metal cations may be provided in gels, colloids,suspensions, dispersions, organic-inorganic compounds, and so on.According to some exemplary embodiments, the metal cations may bestabilized by counterion, e.g., forming an organometallic complex, suchthat they are connected by coordinate bonds rather than by ionic bonds.

The solvents that may be used in the ink composition include, but arenot limited to, alcohols, water, toluene, dioxane, cyclohexanol,Dimethyl sulfoxide (DMSO), formamides, ethylene glycol, propyleneglycol, glycerol, propylene carbonate, and acetonitrile. In someembodiments, the ink composition can contain other additives such as,but not limited to, organic molecules, polymers, conductive polymers,carbon nanotubes (CNT), densifiers, surfactants, and the like. Suchadditives can be used to change the viscosity.

The ratio between metal containing compound/metal cation and theconcentration of solvents is determined based on the type of the metalbeing used in the solution. The ratio between the solvents in themixture can be set for different compositions. That is, concentration ofthe metal cations in the ink composition can be adjusted based on theratio between the solvent mixture and the metal cations. In someembodiments, the concentration of the metal cations in the inkcomposition range between 1% wt. and 70% wt. The entire fraction of thesolvent in the ink composition is 100% wt., regardless of the number ofsolvents in the composition.

That is, in a non-limiting embodiment, when one solvent is used, theentire fraction of the solvent is 100% wt. In another embodiment, when amixture of two solvents is contained ink composition, the first solventranges between 75 wt. % and 99 wt. % and a second solvent ranges between25 wt. % and 1 wt. %, respective of the first solvent. For example, ifthe first solvent is 75 wt. %, then the fraction of the second solventis 25 wt. %. In another non-limiting embodiment, when a mixture of threesolvents are contained in the ink composition, then the fraction of thefirst solvent can range between 75 wt. % and 99 wt. %, the secondsolvent can range between 1 wt. % and 25 wt. %, and the third solventcan range between 1 wt. % and 25 wt. %, with the total percentage ofsolvent being 100 wt. %.

In yet another embodiment, the solvent mixtures consist of two differenttypes of solvents: a high surface tension solvent and a low surfacetension solvent. Examples for a low surface tension solvent include anyalcohol-based solvent, while examples for a high surface tension solventinclude a DMSO solvent.

According to one embodiment, the ink composition has a viscosity rangesbetween 0.001 and 0.5 Pa-s (pascal-second). It should be thereforeappreciated that with such viscosity the ink composition can be appliedor printed on the substrate by means of inkjet printing.

NON-LIMITING EXAMPLES

Following are a few non-limiting examples for ink compositions andforming thin metal films using such compositions.

In a first example, the ink composition includes metal cations AgNO₃ inthe concentration of 40 wt. % in water (solvent). This ink compositionis silver-based.

Using this ink composition, a silver thin film can be formed on a PETsubstrate through the following process. A PET substrate is firsttreated by an Oxygen plasma with the exposure parameters RF frequency,power, and gas flow rate of the Oxygen plasma are respectively set tothe following values: 13 MHz, 50 W, and 5 SCCM Oxygen flow rate. Theplasma is applied in a vacuum chamber with a low pressure (e.g., 375Torr) for 5 minutes through a polymer mask with a void area of 2×2 mm tocreate a hydrophilic pattern.

The silver-based ink composition is then drop-casted on the treated PETsubstrate, so that the ink distribution on the substrate follows thepattern. Then, the PET substrate with ink composition is placed in avacuum chamber and exposed to Argon plasma. The chamber is set with thefollowing exposure parameters RF frequency, power, gas flow rate, andtime having the values: 13 MHz, 50 W, 3 SCCM gas flow rate, and 1minute, respectively. The pressure at the chamber is 375 Torr. As aresult, a patterned (silver 2×2 mm square) metal film having thicknessof 500 nm (nanometer) on top of the PET substrate without any substratedeformation.

As a second example, the ink composition is made of metal cations HAuCl₄in concentration of 10 wt. % in a mixture of solvents. The mixtureincludes water and ethanol at a ratio of 90:10 wt. % (water:ethanol).This ink composition is gold-based.

Using this ink composition, a gold thin film can be formed on a siliconsubstrate through the following process. The silicon substrate is firsttreated as discussed above with reference to the first example. Here,the exposure time is 5 minutes. Then, the ink composition is drop-castedon the silicon substrate through a polymer mask with a square-shapedvoid of 5×5 mm to create a square pattern. The silicon substrate withthe mask and ink composition are placed in a vacuum chamber and exposedto Argon plasma. The exposure parameters RF frequency, power, gas flowrate, and time are set to 13 MHz, 100 W, 3 SCCM, and 1 minute,respectively. The pressure at the chamber is 375 Torr. As result, asquare pattern of a gold metal film having thickness 150 nm is formed ontop of the silicon substrate without any substrate deformation.

To thicken the formed film, an additional layer of the ink compositionis drop-casted on the silicon substrate through the same polymer maskand placed in the vacuum chamber for another Argon plasma exposure cyclerepeated at the same exposure parameters' values as in the first cycle.As a result, the thickness of the formed patterned gold film is 300 nm.

As a third example, the ink composition includes metal cations ofCu(NO₃)₂ in concentration of 5 wt. % in solvent mixture. The solventmixture include water and DMSO at a ratio of 90:10 wt. % (water:DMSO).This ink composition is copper-based.

In this example, a copper film is formed on a glass substrate covered byPEDOT-PSS polymer. The ink composition is drop-casted on the substratethrough a mask with a square-shaped void having an area of 2×2 mm andexposed to Argon atmospheric plasma using a plasma jet. The exposureparameters RF frequency, power, gas flow rate, and time are set 100 kHz,400 W, and 5 SCCM gas flow rate, and 5 seconds, respectively. As aresult, a square-shaped copper film having an area of 2×2 mm and athickness of 120 nm is formed on the glass substrate.

As a fourth example, an ink composition including metal cations of AgNO₃at a concentration of 3 wt. % in a solvent mixture of water, 2-propanol,and DMSO at a ratio of 80:15:5 wt. % (water:2-propanol:DMSO). This inkcomposition is sliver-based.

Using this ink composition, a sliver thin film can be formed on a PETsubstrate through the following process. The PET substrate treated byatmospheric plasma jet applying Oxygen plasma. The exposure parametersRF frequency, power, gas flow rate, and time are set to 40 kHz, 300 W,10 SCCM oxygen flow rate, and 10 seconds, respectively. Then, a patternof hydrophobic lines 500 μm width is created. The ink composition isprinted on the PET substrate following the pattern lines using anink-jet printer. The printed ink lines are exposed to Argon atmosphericplasma using a plasma jet. The exposure parameters RF frequency, power,gas flow rate, and time of the plasma jet are now set to 40 kHz, 300 W,5 SCCM flow rate, and 15 seconds. As result, a patterned silver metalfilm with line width of 500 μm and thickness of 70 nm is formed on thesilicon substrate.

As a fifth example, the composition includes metal cations AgNO₃ at aconcentration of 25 wt. %, CNT at a concentration of 0.02 wt. %, and asolvent mixture. The solvent mixture is of ethanol and water at a ratioof 95:5 wt. % (ethanol:water). The ink composition is printed as apattern of lines using an ink-jet printer. The printed ink lines areexposed to Argon atmospheric plasma applied using a plasma jet. Theexposure parameters RF frequency, power, gas flow rate, and time of theplasma jet are set to 13.54 MHz, 20 W, 5 SCCM argon flow rate, and 5seconds, respectively. As a result, a pattern of silver metal film withline width of 500 μm and thickness of 200 nm is formed on the PETsubstrate.

FIG. 4 shows a scanning electron microscope (SEM) image of a silvermetal film formed on Silicon substrate according to an embodiment. Thefilm thickness is 150 nm. The plasma used in the second phase is Argonand the exposure time is about 1 minute.

FIG. 5 shows a SEM image of a gold metal film formed on a PET substrateaccording to an embodiment. The plasma used in the second phase is Argonwith exposure parameters RF frequency, power, gas flow rate, and time ofthe plasma jet set to gold film: 13.54 MHz, 5 SCCM argon flow, 30 W, 1minute, respectively. The formed gold metal film having thickness is 200nm.

The embodiments have been described in detail referring to the aboveexamples. It should be appreciated that the disclosed embodiments arenot limited to the examples described above, and details of the variousembodiments may be variously modified.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations are generally used herein as a convenient method ofdistinguishing between two or more elements or instances of an element.Thus, a reference to first and second elements does not mean that onlytwo elements may be employed there or that the first element mustprecede the second element in some manner. Also, unless stated otherwisea set of elements comprises one or more elements. In addition,terminology of the form “at least one of A, B, or C” or “one or more ofA, B, or C” or “at least one of the group consisting of A, B, and C” or“at least one of A, B, and C” used in the description or the claimsmeans “A or B or C or any combination of these elements.” For example,this terminology may include A, or B, or C, or A and B, or A and C, or Aand B and C, or 2A, or 2B, or 2C, and so on.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the disclosed embodiment and the concepts contributed by the inventorto furthering the art, and are to be construed as being withoutlimitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosed embodiments, as well as specific examplesthereof, are intended to encompass both structural and functionalequivalents thereof. Additionally, it is intended that such equivalentsinclude both currently known equivalents as well as equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure.

What is claimed is:
 1. An ink composition for forming a patterned thinmetal film on a substrate, comprising: metal cations; and at least onesolvent, wherein the patterned thin metal film is adhered to a surfaceof the substrate upon exposure of the at least metal cations to alow-energy plasma.
 2. The ink composition of claim 1, wherein atemperature of the surface of the substrate upon exposure to thelow-energy plasma is between 50° C. and 70° C., inclusive.
 3. The inkcomposition of claim 1, further comprising: counterions organic ligandsfor stabilizing the metal cations.
 4. The ink composition of claim 1,further comprising: at least one additive for increasing the viscosityof the ink composition.
 5. The ink composition of claim 4, wherein theat least one additive is any of: organic molecules, polymers, conductivepolymers, carbon nanotubes (CNT), densifiers, and surfactants.
 6. Theink composition of claim 4, wherein ink composition has a viscositybetween 0.001 Pa-s and 0.5 Pa-s, inclusive.
 7. The ink composition ofclaim 1, wherein the ink composition is in a form of any of: a solution,a dispersion, a suspension, a gel, and a colloid.
 8. The ink compositionof claim 1, wherein the metal cations are selected from the groupconsisting of: M(NO3)_(n), M(SO₄)_(n), MCl_(n), and H_(m)MCl_(n+m),wherein “M” is a metal atom with a valence of “n”, H is hydrogen, NO₃ isnitrate, SO₄ is sulfate, Cl is chloride, and “m” is a valence of acounter ion.
 9. The ink composition of claim 8, wherein the metal atomis at least any of: gold, silver, copper, and metal alloy.
 10. The inkcomposition of claim 1, wherein a concentration of the metal cations isbetween 1 wt. % and 70 wt. %, inclusive.
 11. The ink composition ofclaim 1, wherein the at least one solvent is any of: alcohol, water,toluene, Dimethyl sulfoxide (DMSO), formamides, ethylene glycol,propylene glycol, glycerol, propylene carbonate, and acetonitrile. 12.The ink composition of claim 1, wherein the at least one solvent is amixture of at least two types of solvents.
 13. The ink composition ofclaim 12, wherein the at least two types of solvents include at least ahigh surface tension solvent and a low surface tension solvent.
 14. Theink composition of claim 1, wherein the at least one solvent includes100 wt. % of one type of solvent.
 15. The ink composition of claim 10,wherein the metal cations include AgNO₃, wherein the at least onesolvent includes 100 wt. % of one type of solvent.
 16. The inkcomposition of claim 15, wherein the concentration of the metal cationsAgNO₃ is 40 wt. %, wherein the at least one solvent is water.
 17. Theink composition of claim 10, wherein the metal cations include HAuCl₄,wherein the at least one solvent is a mixture of solvents.
 18. The inkcomposition of claim 15, wherein the concentration of the metal cationsHAuCl₃ is 40 wt. %, wherein the at least one solvent includes water andethanol, wherein the ratio of water to ethanol is 90:10 wt. %.
 19. Theink composition of claim 1, wherein the metal cations include Cu(NO3)₂,wherein the at least one solvent is a mixture of solvents.
 20. The inkcomposition of claim 17, wherein the concentration of the metal cationsis 5 wt. %, wherein the mixture of solvents includes water and Dimethylsulfoxide (DSMO), wherein the ratio of water to DSMO is 90:10 wt. %. 21.The ink composition of claim 10, wherein the metal cations includeAgNO₃, wherein the at least one solvent is a mixture of solvents. 22.The ink composition of claim 19, wherein the concentration of the metalcations is 3 wt. %, wherein the mixture of solvents includes water,2-propanol, and Dimethyl sulfoxide (DMSO), wherein the ratio of water to2-propanol to DMSO is 80:15:5 wt. %.
 23. The ink composition of claim10, wherein the metal cations include AgNO₃, wherein the at least onesolvent is a mixture of solvents.
 24. The ink composition of claim 19,wherein the concentration of the metal cations is 25 wt. %, wherein themixture of solvents includes ethanol and water, wherein the ratio ofethanol to water is 95:5 wt. %.
 25. The ink composition of claim 1,wherein the substrate is any one of: an organic substrate, an inorganicsubstrate, a hybrid organic-inorganic substrate, a ceramic substrate, asilicon substrate, and a glass substrate.
 26. The ink composition ofclaim 1, wherein the substrate is any one of: a polyethyleneterephthalate (PET) substrate, a polyimide substrate, and a polyethylenenaphthalate (PEN) substrate.
 27. The ink composition of claim 1, whereinthe low-energy plasma is an inert gas plasma.
 28. The ink composition ofclaim 1, wherein the low-energy plasma includes at least any of: anArgon plasma, a Nitrogen plasma, and an Oxygen plasma.
 29. The inkcomposition of claim 1, wherein the ink composition is applied on thesubstrate by means including at least any of: drop-casting,spin-coating, spray-coating, immersion, flexography, gravure, inkjetprinting, aerosol jet printing, and contact imprinting.